*4 Gravitation. [Book I. 



they could obferve the form of the plant in the cry- 

 ftallized mafies. Later philofophers have afcribed to 

 the primary parts of bodies a certain property which 

 they call -polarity (as analogous to that property of the 

 magnetic needle) and which difpofes them to fhoot out 

 in certain directions *. A more probable opinion ap- 

 pears to be, that the minute particles of each cryftal- 

 lizing body are of fuch a form that the fides, which 

 approach in contact, difpofe them in a particular di- 

 rection. 



From this regular arrangement of the parts it refults 

 that homogeneous bodies poflefs always an equal den- 

 fity in all their parts ; and in mod cafes, if nature is 

 interrupted in the procefs, the concrete will be imper- 

 fectly formed. So nice and critical is the arrange- 

 ment of the parts in fonorous bodies, that it is faid the 

 fmalleft vibration of the air occurring during the ope- 

 ration of calling a bell, or racher while the metal is 

 fettling in the mould, even the barking of a dog, will 

 injure the tone f . 



III. The attraction of GRAVITATION materially dif- 

 fers from the two preceding fpecies of attraction, fince 

 it requires neither the particles of the bodies, nor the 

 bodies themfelves, to be brought into immediate con- 

 tact, but acts at confiderable diftances, and in this re- 

 Jpect it is analogous to the attraction of magnetifm 

 and electricity. 



The moft obvious effect of gravitation is the gene- 

 ral tendency of bodies to the furface, or perhaps to the 

 center of the earth. It appears to be one of the great 

 laws of gravitation, that the attraction of bodies is in 

 proportion to the quantity of matter they contain. 

 The earth, therefore, being fuch an immenfe aggre- 



* Jones's Phyfiolog. Difquif. 22. f Ibid. 



gate 



